Optical fibers have been widely used for the propagation of optical signals, especially to provide high-speed communication links. Optical links using fiber optics provide various advantages over electrical links, for example, comparatively large bandwidths, comparatively high noise immunity, comparatively reduced power dissipation, and comparatively minimal crosstalk. Optical signals carried by optical fibers may be processed by a wide variety of optical and/or optoelectronic devices, including integrated circuits.
Photonic integration is playing an increasingly important role in optical systems. Photonic integration may provide various benefits, such as a relatively smaller footprint, higher port density, reduced power consumption, and reduced cost, which may render photonic integration a promising technology for building the next generation of integrated optical devices, such as wavelength-division multiplexing (WDM) transponders, transceivers, and other types of devices. Photonic integration requires the optical coupling between an optical waveguide and an optical fiber to realize optical signal inputs and/or outputs, for example, coupling the end of an optical fiber to the surface of a photonic integrated circuit (PIC). This interface coupling is a critical technology to reduce the optical signal loss in integrated optical system.